Re: [PATCH v3 1/3] mm: mprotect: always skip dma pinned folio in prot_numa_skip()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Wed, Oct 15, 2025 at 08:35:14PM +0800, Kefeng Wang wrote:
> If the folio(even not CoW folio) is dma pinned, it can't be
> migrated, so always skip pinned folio to avoid a waste of cycles
> when folios migration.

NIT: 'when folios migration' -> 'when folios are migrated'.

Maybe worth saying 'due to elevated reference count?'

>
> Reviewed-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Lance Yang <lance.yang@linux.dev>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>

LGTM though so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  mm/mprotect.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 113b48985834..bb59a42809b8 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -136,9 +136,12 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
>  	if (folio_is_zone_device(folio) || folio_test_ksm(folio))
>  		goto skip;
>
> -	/* Also skip shared copy-on-write pages */
> -	if (is_cow_mapping(vma->vm_flags) &&
> -	    (folio_maybe_dma_pinned(folio) || folio_maybe_mapped_shared(folio)))
> +	/* Also skip shared copy-on-write folios */
> +	if (is_cow_mapping(vma->vm_flags) && folio_maybe_mapped_shared(folio))
> +		goto skip;
> +
> +	/* Folios are pinned and can't be migrated */
> +	if (folio_maybe_dma_pinned(folio))
>  		goto skip;
>
>  	/*
> --
> 2.27.0
>
>